1. Field of the Invention
The present invention relates to an apparatus for use in the ammonia soda process or the ammonium chloride soda process.
2. Description of the Prior Art
The solutions treated in the ammonia soda process or the ammonium chloride soda process include ammoniacal brines, mother liquors formed in a carbonation tower (hereinafter referred to as carbonation mother liquors) and ammonium chloride mother liquors. These solutions have high contents of NaCl, NH.sub.4 Cl, NH.sub.4 OH, NH.sub.4 HCO.sub.3, NaHCO.sub.3 and the like. Accordingly, the corrosiveness of these solutions is quite high resulting in corrosive environments for both processes which are similar.
The principal apparatus for treating these process solutions are carbonation towers, rotary vacuum filters, ammonia absorbers, salting-out crystallizers, cooling crystallizers, ammonia recovery towers and the like. Various materials have been tested and employed for use in these apparatus as in those portions which contact the corrosive solutions. However, a satisfactory anticorrosive material has not yet been obtained. For example, a conventional austenitic stainless steel cannot be used in the cooling tube of a carbonation tower because of this material's inferior localized anti-corrosive properties. It is known that aluminum-silicon cast iron containing several percent of aluminum and silicon, has highly anti-corrosive properties. Unfortunately, it is disadvantageously hard to mold aluminum-silicon cast iron into proper shape for a cooling tube because of the nature of the moldability of cast iron. In the past, a calorizing steel has been widely used for preparing the cooling tube because of the low initial cost involved. However, cooling tubes made of this calorizing steel have short lifetimes because of extensive pitting. As a result, frequent replacement is required, greatly increasing both the cost and difficulty of operation. Consequently, it can be seen that a need continues to exist for an anticorrosive material for use in these apparatus.